In some applications there is a need to provide a range of different DC power supply voltages to meet the power supply requirements of different equipment modules. As an example, in the field of communication apparatus, there is typically a 48V DC supply and modules can have power supply requirements selected from the range: 12V, −12V, 1.04V, 1.2V, 1.8V, 2.5V, 3.3V, 5V. Different power supply voltages may be required to meet the differing demands of analog devices, digital devices, semiconductor technologies etc.
The architecture of a power conversion system for telecom applications typically comprises a small number of primary DC-DC converters providing medium voltage levels from the main DC voltage source (typically 48V), and several point-of-load converters (secondary conversion), one for each output voltage, to achieve the lower voltages. Typically, there is a first (isolated) conversion from −48V to an intermediate voltage, such as 12V or 3.3V, and then several points of load which converts this continuous voltage to the needed low voltages (typical example of secondary supply rails: +/−12V @ 2.2 A; +3.3V @ 6 A; +1.8V @ 6 A; +1.2V @ 6 A; +1.04V @ 13 A). FIG. 1 shows an example of a conventional power conversion architecture.
A disadvantage of the existing approach to designing a multiple output DC-DC converter is that it can deliver a poor conversion efficiency, because the converter cascades multiple stages of conversion. For example, with three cascaded conversion stages, each having a conversion efficiency of 0.9, there is an overall conversion efficiency of 0.9*0.9*0.9=0.729. This approach also requires a very large number of components for the multiple conversion stages of the DC-DC converter, and the associated high cost and large physical size of a converter having multiple conversion stages.